Chairs having adjustable armrests and/or backrests are highly desirable because they can be readily conformed to the body proportions and dimensions of the individuals using the chair. Such chairs can also be readily customized to provide the greatest comfort to the user in relation to the specific station at which the individual is working. Because of the universality of such adjustable chairs, one model may be sold to a wide variety of consumers, and for that reason production costs are significantly reduced. In summary, adjusting mechanisms for chairs permit selection of the height for seats, armrests and/or backrests. Various prior art mechanisms are presently available for accomplishing these adjustments.
One such prior known arrangement connects the component to be adjusted, such as the seat of a chair, to a base with a threaded rod that meshingly engages a threaded supporting block which is fixedly secured to the base. To adjust the height of the seat, the operator turns the seat with respect to the base and the seat is raised or lowered depending on the direction of rotation. The sensitivity of the adjustment depends on the angular inclination of the threads. Threaded rods, however, are not practical adjusting devices for all chair components not only because of their bulk but also because components such as armrests and backrests cannot be easily rotated.
Another known approach for adjusting the height of a chair component is to have one portion of a support member slidably received on another portion of the support member and provide a clamp to hold the two portions of the support member together. One such device utilizes a base column with a sleeve slidably disposed over the base column. A bolt is threadably received in the sleeve, and a handle is connected to the bolt. To lock the position of the sleeve with respect to the base column, the operator tightens the bolt against the column. To adjust the height of the sleeve, the bolt is loosened, the sleeve adjusted, and the bolt re-tightened. Devices employing such restraining means are undesirable because the degree of restraint depends on the force used to tighten the bolt.
One attempt to solve this problem has resulted in a base column having a plurality of holes within which the bolt may be selectively received. When the bolt is received in one of the holes, the restraining force is no longer dependant on the force used to tighten the bolt. One problem with this type of device is that the operator must align the bolt that penetrates the sleeve with the holes in the bar in order to adjust the component. The alignment requirement forces the operator to search blindly for the hole with one hand while supporting the weight of the component with the other hand.
Such an arrangement is, therefore, particularly undesirable for use with heavy chair components. Another problem with these devices is the amount of time required for the operator to perform the adjustment. A further problem is that each adjustable component has an unsightly knob protruding therefrom. The knobs must be large enough to provide a good grip tier the operator, but small enough to allow the chair to function. Still a further problem is that the threads in the sleeves can, with misuse, become stripped and render the adjusting mechanism inoperable.
A further attempt to solve the problems inherent in the prior art arrangements has been to incorporate a ratchet assembly in the adjusting mechanism. In these devices, a base structure presents a plurality of teeth which are to be engaged by a pawl. The pawl is mounted on a sleeve that is attached to the chair component. As the chair component is raised, the pawl engages successive teeth until the sleeve reaches its uppermost position. The operator then releases the pawl by pushing a button or operating a lever. When the pawl is disengaged, the sleeve may be lowered to the desired position whereupon the operator re-engages the pawl by releasing the lever or button. Devices incorporating such levers or buttons perform satisfactorily, but two problems of the prior art remain: the requirement that the operator push or manipulate something while making the adjustment; and, the protrusion caused by the lever or button.
The latest known attempt to overcome some of the problems found in the prior art is disclosed by U.S. Pat. No. 4,639,039 to Donovan. The Donovan device incorporates a ratchet mechanism that is set and reset when the device is translated between two limiting positions. One undesirable aspect of the Donovan device is that the complexity of the mechanism is such that it can only be of a size which prevents it from being unobtrusively built into the components of a chair. Thus, the appearance of the chair must be altered to incorporate the Donovan device. Another undesirable aspect of the device has been the cost and the relative difficulty of manufacturing all of the elements of the device.